Electrically driven self-contained in-tank rotary fuel pumps have been used for delivering gasoline from a supply tank to an internal combustion engine of a motor vehicle. This type of pump produces a steady, non-surging, highly pressurized flow of fuel making it ideal for use with modern fuel injection systems. The design is also highly tolerant of fuel supply line pressure transients commonly associated with the abrupt opening and closing of individual fuel injectors.
Typically, these pumps consist of a housing having a fuel inlet cover on one end and an outlet cover at the opposite end. Inside the housing, at least one and sometimes two rotors for imparting motion and momentum to the fuel are mounted on a drive shaft of an armature of an electric motor. In a common design, an intake rotor having a plurality of circumferentially spaced radial impeller vanes and cavities is located adjacent the inlet for drawing fuel from the tank. During operation, fuel through an inlet passage of the inlet cover is suctioned into the impeller cavities and propelled circumferentially in the direction of rotor rotation. A second rotor receives fuel from the first impeller and forcibly expels it from the pump to the engine.
However, during operation, as each cavity of the intake rotor passes over the inlet, centrifugal force acting on fuel within the cavity displaces some of the fuel back into the inlet causing turbulence to and vaporization of the incoming fuel, reducing the amount of fuel entering the pump and decreasing pump flow rate and efficiency while increasing the electrical energy demand of the motor.